This invention relates to a holder for drill instruments and particularly to a chuck assembly for facilely centering and holding drill bits illustratively for use in drill sharpening and milling machines.
The art of chuck design has progressed to the extent that a variety of chucks are presently available for use in virtually all machines involving drilling. A substantial percentage of such chucks function on the principle that a plurality of jaws are adjustably opened and closed to receive and embrace the shank of the drill for a desired sharpening, milling or general drilling operation. An example of such a chuck in widespread use is found in a conventional hand drill and it generally employs three jaws for holding a drill.
For precision work, time-consuming procedures as well as complicated and expensive chucks are required to provide for highly accurate centering and holding of a drill bit. The procedures typically involve measurements of, for example, angular alignment of a drill within the chuck. Inaccurate alignment of the shank or fluted segments of a drill within the embrace of the chuck jaws as a result of improper procedures or inherently nonprecise chucks usually results in problems such as incorrect angular sharpening of the drill, undesired errors in milling or drilling by milling or drilling machines, and even the fracture or breaking of the drill itself.
The latter problems assume major proportions in using small diameter, or micro, drills. The term microdrill is used to designate a small diameter drill, for example, ranging from approximately 0.060 of an inch down to 0.001 of an inch in diameter. These drills are, for example, designated by 0.001 diameter sizes.
A long recognized deficiency in the prior art has been that no facilities have heretofore been available for simply and economically enabling microdrills to be resharpened after its lip edge has been dulled, impaired or broken by usage. As a consequence, it has been a customary practice in the art to discard such drills despite the fact that they could be resharpened if facilities were available to do so. Obviously, such a practice is costly and wasteful.
A principal factor contributing to such inadequacies in the prior art has been the nonprecise centering and embracing of drills within the jaws of available chucks. A long-felt need therefore has existed for improvements in chucks especially those suitable for use with microdrills.